[burfog]

I can see that Texas A&M made you use graphite, but otherwise I don't see why the nozzle must be made out of graphite.

For a turbine blade, you'd use a single-crystal superalloy. The machining is just 3D printing of wax; you then use a lost-wax process to cast it. Cooling channels are built into it.

That ought to work. You don't even need a particularly corrosion-resistant superalloy if you cool it with liquid methane and then let that leak out to form a moving film on the surface.

[ThenAsNow]

Regeneratively cooling nozzles (i.e., circulating liquid or gaseous propellant in embedded cooling channels) is standard fare for liquid rocket engines. GP used graphite because it was a student project. Probably not what would be done for a real launch vehicle.

One thing to keep in mind about spike nozzle cooling is that you get compression shocks from the aerospike flowfield that strike the centerbody. These shock impingements drive up local heat transfer rates. As the flowfield changes with increasing altitude (decreasing ambient pressure), the impingement locations move. So when you size your cooling capacity, you have to account for this which tends to make the spike "overcooled" as compared to what you'd have to design for with the bell. This tends to correlate with increased pressure losses from the associated high coolant flow rates, causing a system-level mass hit and detracting from the nozzle Isp efficiency benefit. Take a look at XRS-2200 test video to watch the spike ramps ice over hard after engine shutdown. While not unique to that engine, the magnitude of that effect has a lot to do with how heavily cooled the ramps were.

[avmich]

> Cooling channels are built into it.

How would you build cooling channels into something like this?

[burfog]

Rolls Royce blade production: https://www.theengineer.co.uk/rolls-royce-single-crystal-tur...

Picture of blade and some process description: https://en.wikipedia.org/wiki/Turbine_blade

Picture of wax blade without cooling channels: https://en.wikipedia.org/wiki/Investment_casting

Company that uses DLP 3D printing for turbine blades: https://www.prodways.com/en/lost-wax-casting-of-turbine-blad...

[ThenAsNow]

Conventional ways to do this include casting or, as is done on the RL-10 and SSME, building the nozzle out of thin-walled tubes (very labor-intensive and expensive). 3D printing is the future here, but there's still lots of improvement required in terms of wall thickness and roughness control, not to mention build volume.

[avmich]

The previous phrase was that the part is lost-wax cast. To me it's interesting how one can build cooling channels in the part which is cast.